The Central Northern Adelaide Health Service and Southern Adelaide Health Service are to merge, with as many as 100 jobs likely to go.

SA Health CEO Dr Tony Sherbon says the restructuring will take effect from July 1, achieving more efficient administration and less duplication.

"This enables us to direct our resources to clinical services in preference to administration," he said.

Savings of up to $4 million per year have been promised.

SA Opposition's health spokesman Duncan McFetridge says having two authorities was a recommendation of a health review.

"These regions were created five years ago, millions of dollars was spent and now we're seeing it undone," he said.

The Central Northern Adelaide Health Service has 15,000 staff and the southern service has 7,000.

The merged service will continue to deliver public pathology services, BreastScreen SA and the SA Dental Service.

Australian Medical Association (AMA) president Dr Andrew Lavender says the changes could reduce delays being caused by too much bureaucracy.

"We'll be watching to make sure that any administration is as lean as possible and as much resources as possible are focused on giving delivery at a clinical level for the communities," he said.

Health Minister John Hill has promised no reduction in health services as a result of the merger.

He says it is likely the AMA's suggestions to cut high-paid administrative jobs and reorganise services will be acted on.

"At the end of this we'll have three regions - one for country, which is working very well, one for the metropolitan area and children's, youth and women's network which covers the whole state and I think that's a very logical way of arranging things," he said.